1. Field of the Invention
The present invention relates to an image recording apparatus for recording an image on a recording medium by applying light from a spatial light modulator of diffraction grating type.
2. Description of the Background Art
In recent years, a spatial light modulator (hereinafter, referred to as “SLM (Spatial Light Modulator)”) of reflection type has been used for forming an image on a screen of a display system for so-called e-cinema where a movie is reproduced from digitized movie information. Such a reflection type SLM has been used to record an image with light in printing and plate-making equipment.
A reflection type SLM controls ON/OFF of each device element corresponding to pixels of an image to be projected, and light is modulated spatially. As a typical reflection type SLM where device elements are arranged two-dimensionally, a digital micromirror device (DMD) has been known. A grating light valve (GLV (registered trademark)) has been known as a typical reflection type SLM where device elements are arranged one-dimensionally.
For the DMD, tiny mirrors are arranged two-dimensionally and light is modulated spatially by inclining each mirror separately. On the other hand, the GLV is a reflection type SLM of diffraction grating type, where several thousands of fine ribbons for reflection are arranged, and light is diffracted by changing height of a reflection surface of every other ribbon with electric force. In a case where electric force does not exert on the ribbons, zeroth order light (zeroth order diffracted light) of incident light is obtained as normally reflected light. In a case where electric force exerts on the ribbons, +/− first order diffracted lights (hereinafter, referred to as “first order diffracted light”) are guided. Normally, the zeroth order light is signal light for recording an image, and the first order diffracted light is eliminated as non-signal light.
In the meantime, a method called computer to plate (hereinafter, referred to as “CTP”) has been generally known in the recent printing and plate making industry, where direct-imaging is performed on a photosensitive material which is a thermal recording medium. In the CTP, it is desired that, from the viewpoint of sensitivity of a photosensitive material, light as strong as possible should be guided to the photosensitive material. When the GLV is used in the CTP, first order diffracted light having almost the same amount of light as zeroth order light is generated, and thus it is important to remove the first order diffracted light sufficiently.
This matter is especially important in an optical system where the GLV and a high-power laser are used, and for example, Japanese Patent Application Laid Open Gazette No. 2003-140354 discloses a technique for removing heat caused by heat blocking by guiding unnecessary non-signal light or light from a light source in non-exposure to a jacket for cooling.
When first order diffracted light is vignetted inside a projection optical system for projecting light from the GLV onto a photosensitive material, unnecessary light is complicatedly irradiated to an inner surface of a lens barrel or a plurality of optical parts. As a result, for example, fluctuation of signal light occurs due to rise of temperature of lenses or metal fittings, and this causes problems, such as degradation or instability in output quality, damage on lenses, or the like.